The present invention pertains to the treatment of a paper web which is subsequently corrugated to form the fluted medium in the manufacture of corrugated paperboard. More particularly, the present invention pertains to an apparatus and method for drying a shallow surface layer of the premoistened web immediately prior to entry into the corrugating nip.
In the manufacture of corrugated paperboard, the corrugated medium is formed by passing the paper web through the nip formed by a pair of counterrotating fluted corrugating rolls. Upstream of the corrugating nip, the medium web is heated and premoistened to enhance the formability of the flutes by the corrugating rolls. In a typical preheater, the web is heated by passing it around a heated roll with moisture applied either by a water spray or the application of steam. The premoistened web is transferred directly into the corrugating nip and the fully moistened web permits the flutes to be formed therein without rupturing the web. However, the moisture in the web surface layers significantly increases the coefficient of friction of the web surface. This in turn directly affects the corrugating process because increased friction between the paper and the flutes of the corrugating rolls results in a significant tension increase in the medium web as it moves through the labyrinth of the fluting process.